U.S. patent application number 14/177133 was filed with the patent office on 2014-08-14 for apparatus for transcutaneous electrical stimulation of the tibial nerve.
This patent application is currently assigned to Neurowave Medical Technologies LLC. The applicant listed for this patent is Neurowave Medical Technologies LLC. Invention is credited to Aftab Ahmad, Matthew J. Geary, Farhan Hussain.
Application Number | 20140228927 14/177133 |
Document ID | / |
Family ID | 51297989 |
Filed Date | 2014-08-14 |
United States Patent
Application |
20140228927 |
Kind Code |
A1 |
Ahmad; Aftab ; et
al. |
August 14, 2014 |
APPARATUS FOR TRANSCUTANEOUS ELECTRICAL STIMULATION OF THE TIBIAL
NERVE
Abstract
An electro-acupuncture device for controlling over active
bladder is described. The device includes a housing, circuitry for
generating electro-acupuncture stimulus disposed within the
housing, and at least one strap for securing the housing to the
ankle. The device also includes a pair of D-shaped electrodes
received within the bottom outer surface of the housing. The
housing of the device is flexible with a low profile and is shaped
so that it is conformal to a person's ankle. When the device is
strapped to a patient's ankle, the electrodes contact the ankle and
provide electric stimulation to the tibial nerve within the
ankle.
Inventors: |
Ahmad; Aftab; (Chicago,
IL) ; Geary; Matthew J.; (Chicago, IL) ;
Hussain; Farhan; (Chicago, IL) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Neurowave Medical Technologies LLC |
Chicago |
IL |
US |
|
|
Assignee: |
Neurowave Medical Technologies
LLC
Chicago
IL
|
Family ID: |
51297989 |
Appl. No.: |
14/177133 |
Filed: |
February 10, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61762825 |
Feb 8, 2013 |
|
|
|
Current U.S.
Class: |
607/148 |
Current CPC
Class: |
A61H 39/002 20130101;
A61N 1/0456 20130101; A61N 1/36034 20170801; A61H 2201/164
20130101; A61H 2201/165 20130101; A61H 2205/125 20130101 |
Class at
Publication: |
607/148 |
International
Class: |
A61N 1/36 20060101
A61N001/36 |
Claims
1. A nerve stimulation device for applying electrical stimulation
to a nerve, the nerve stimulation device comprising: a) a housing
having a curved bottom outer surface adapted for application to an
exterior surface of a human body, wherein the housing is configured
to be conformal to the exterior surface of the body; b) at least
two electrodes received through respective apertures of the bottom
outer surface of the housing wherein the electrodes extend
outwardly a given depth from the bottom outer surface of the
housing; and c) a pulse generating circuit enclosed within the
housing operably connected to the electrodes to provide an
electrical pulse to the nerve positioned within the body through
the electrodes.
2. The nerve stimulation device of claim 1 wherein the electrodes
are substantially D-shaped having a straight edge and an arcuate
edge, the electrodes being arranged within the aperture of the
housing with the straight edges opposing each other.
3. The nerve stimulation device of claim 2 wherein the straight
edge of the electrode has a length of about one inch and the
arcuate edge has an inner radius of about one half inch.
4. The nerve stimulation device of claim 1 wherein at least one
strap is attached to the housing, the strap adapted to secure the
housing to the body, and wherein the at least one strap is
configured relative to the housing and the electrodes so that the
electrodes directly contact the skin of the human body and are
disposed longitudinally along the line established by the
nerve.
5. The nerve stimulation device of claim 1 wherein a gasket having
a first gasket aperture and a second gasket aperture dimensioned to
receive the electrodes is disposed about the electrodes on the
bottom outer surface of the housing.
6. The nerve stimulation device of claim 1 wherein the at least two
electrodes are positionable adjacent the tibial nerve.
7. The nerve stimulation device of claim 1 wherein the housing is
composed of a material selected from the group consisting of
silicone rubber, acrylonitrile butadiene styrene, styrene,
polycarbonate, neoprene and combinations thereof.
8. The nerve stimulation device of claim 1 wherein the housing has
a height to width ratio ranging from about 1 to about 3.
9. The nerve stimulation device of claim 1 wherein the housing
comprises an outer edge having a beveled edge.
10. The nerve stimulation device of claim 1 wherein the bottom
surface of the housing comprises a convex shape.
11. The nerve stimulation device of claim 1 wherein the pulse
generating circuit is configurable to emit a constant current
electrical pulse.
12. The nerve stimulation device of claim 1 wherein the electrical
pulse comprises a maximum current output of about 60 milliamps.
13. A nerve stimulation device for applying electrical stimulation
to a nerve, the nerve stimulation device comprising a) a housing
having a convex bottom outer surface adapted to be contactable to
an exterior surface of the ankle of a human body, wherein the
housing is configured to be conformal to the ankle; b) at least two
substantially D shaped electrodes received through respective
apertures of the bottom outer surface of the housing, wherein the
electrodes outwardly extend a given depth from the convex bottom
outer surface of the housing; and c) a pulse generating circuit
enclosed within the housing operably connected to the electrodes to
provide a constant current electrical pulse to the tibial nerve
positioned within the ankle through the electrodes.
14. The nerve stimulation device of claim 13 wherein the
substantially D-shaped electrodes have a straight edge and an
arcuate edge, the electrodes being arranged on the housing with the
straight edges opposing each other.
15. The nerve stimulation device of claim 13 wherein at least one
strap is attached to the housing, the strap adapted to secure the
housing to the ankle, and wherein the at least one strap is
configured relative to the housing and the electrodes so that the
electrodes directly contact the skin of the human body and are
disposed longitudinally along the line established by the tibial
nerve.
16. The nerve stimulation device of claim 13 wherein the at least
two electrodes are positionable adjacent a posterior portion of the
tibial nerve.
17. The nerve stimulation device of claim 13 wherein the housing is
composed of a material selected from the group consisting of
silicone rubber, acrylonitrile butadiene styrene, styrene,
polycarbonate, neoprene and combinations thereof.
18. The nerve stimulation device of claim 13 wherein the housing
has a height to width ratio ranging from about 1 to about 3.
19. The nerve stimulation device of claim 13 wherein the electrical
pulse comprises a maximum current output of about 60 milliamps.
20. The nerve stimulation device of claim 13 wherein a gasket
having a first gasket aperture and a second gasket aperture
dimensioned to receive the electrodes is disposed about the
electrodes on the bottom outer surface of the housing.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority from U.S. Provisional
Patent Application Ser. No. 61/762,825, filed Feb. 08, 2013.
FIELD OF THE INVENTION
[0002] The devices described below relate to the field of
electro-acupuncture and non-invasive stimulation of nerves.
BACKGROUND OF THE INVENTION
[0003] The peripheral nervous system of a human body consists of
the nerves and ganglia outside of the brain and spinal cord. Its
main function is to connect the central nervous system to the limbs
and organs. Unlike the central nervous system, the peripheral
nervous system is not protected by the bone of the spine and the
skull, or by the blood-brain barrier, leaving it available for
non-invasive, peripheral, electrical nerve stimulation.
[0004] Nerves may suffer functional defects due to normal wear and
tear, physical injuries, infection, and/or the failure of blood
vessels surrounding the nerves. Other defects occur with the
inappropriate activation or inhibition of somatic and autonomic
pathways. These functional defects may be accompanied by pain,
numbness, weakness, and in some cases, paralysis. In other cases,
defects may cause undesirable initiation or suppression of
physiological functions such as muscle contraction. Problems may
include urinary or fecal incontinence. For example, with urinary
incontinence, daily physical activities such as laughing, coughing,
and sneezing may result in involuntary urination. Similarly,
inappropriate contraction and relaxation of muscles that control
bladder functioning may result in unplanned and undesired
urination.
[0005] OAB is a urological condition defined by a set of symptoms
that include urgency, with or without urge incontinence, and is
usually accompanied by frequency and nocturia. Frequency is defined
as urinating more than 8 times a day. In people with OAB, the
layered, smooth muscle that surrounds the bladder (detrusor muscle)
contracts spastically, sometimes without a known cause, which
results in sustained, high bladder pressure and the urgent need to
urinate. Normally, the detrusor muscle contracts and relaxes in
response to the volume of urine in the bladder and the initiation
of urination. People with OAB often experience urgency at
inconvenient and unpredictable times and sometimes lose control
before reaching a restroom.
[0006] Accordingly, urge incontinence and overactive bladder
interfere with work, daily routine, and the like; causes
embarrassment; and can diminish self-esteem and quality of
life.
[0007] There are a variety of treatment options for OAB.
Conservative treatment starts with bladder training techniques,
such as education, timed voiding, restriction of fluid intake, and
distraction/relaxation. These can be combined with pelvic floor
training exercises that are intended to strengthen and support the
pelvic floor muscles. A number of medications are effective for
treating OAB. Anticholinergic (antimuscarinic) agents and agents
with mixed anticholinergic and bladder wall effects are widely
prescribed for OAB. Numerous randomized, controlled trials and
systematic reviews have established that these drugs have efficacy
over placebo, but the magnitude of benefit in reducing OAB symptoms
is modest; a substantial number of patients will not achieve
adequate symptom relief, and there are relatively high rates of
adverse effects. For patients with OAB refractory to standard
treatments, more invasive treatment options are available, such as
intravesicular administration of botulinum toxin A, sacral nerve
stimulation, or augmentation cytoplasty.
[0008] Another technique for overcoming the urge incontinence or
OAB involves stimulating either the sacral or tibial nerve by using
an electric or magnetic impulse. This is commonly referred to as
transcutaneous or percutaneous nerve stimulation. One such
electro-medical device capable of providing the required stimuli is
commonly referred to as an implantable Pulse Generator (IPG). An
IPG typically includes one or more electrodes, an electrical pulse
generator, a battery, and a housing. The electrical pulse generator
generates a waveform having a specific shape, form, and frequency
range capable of stimulating a target nerve. When the electrodes
receive the waveform from the generator, they draw energy from the
battery and generate an electric field of suitable strength to
stimulate the target nerve.
[0009] IPGs are typically used for stimulating the sacral nerve and
have proven to be somewhat effective. One of the problems
associated with IPGs, however, is that implanting the device is
invasive, and may cause undesirable complications during and after
implantation. Documented complications associated with the
implantation procedure include bleeding, infection, or tissue
damage. Documented complications after the implantation procedure
include generator and/or lead failures. Sometimes a complication
may require removal of the device, and re-implantation of a new
device.
[0010] Another technique commonly used to provide the required
impulse is electro-acupuncture nerve stimulation.
Electro-acupuncture nerve stimulation involves passing a small
electric current between pairs of acupuncture needles. The needles
may provide electrical nerve stimulation percutaneously or
subcutaneously. Both approaches involve inserting needles (also
called the electrodes) into the prescribed acupuncture or trigger
points so that the external parts of the needles can be secured
against the skin of the patient. Both approaches require the
patient to go to a clinic for clinician insertion of the needles
into the skin. Additionally, patients have been known to experience
some discomfort with these approaches. Furthermore, the known
device exhibits some difficulty in use and precision control of the
procedure because it is impossible to change a position of the
inserted electrode in the body without compromising needle
sterility or without removing the whole electrical assembly.
[0011] Posterior tibial nerve stimulation (PTNS) is the least
invasive form of neuromodulation used to treat OAB and the
associated symptoms of urinary urgency, urinary frequency and urge
incontinence. PTNS is a type of neuromodulation therapy that uses
electrical stimulation to target specific nerves in the sacral
plexus that control bladder function. Specifically, tibial nerve
stimulation targets the nerves of the pelvic floor with gentle
electrical impulses to alter the activity of the bladder. The
treatment targets the sacral plexus from an accessible minimally
invasive entry point into the nervous system. These urinary
symptoms may also occur with interstitial cystitis and following a
post-radical prostatectomy. Outside the United States, PTNS is also
used to treat fecal incontinence. PTNS has been shown to be
effective as a primary therapy. However, treatment for Overactive
Bladder and Fecal Incontinence many times begins with conservative
therapies including pharmacology. Nearly 80% of patients
discontinue use of drugs within the first year, many due to adverse
side-effects. Neuromodulation is emerging as an effective modality
to treat patients who are not successful with pharmacologic
methods.
[0012] Since the introduction of PTNS, many published studies have
demonstrated PTNS efficacy in treating OAB symptoms. Ridout et al.
in W. J. Obstet Gynaecol 2010; 30(2) published a literature review
evaluating evidence of PTNS for overactive bladder syndrome. The
authors found that PTNS may have a role as a useful, minimally
invasive treatment option in medically refractory OABS with a
60-81% response rate. However, there is insufficient data to
advocate PTNS as a first-line treatment due to its cost and
long-term treatment regimen. This invention addresses the cost and
treatment method by providing an alternative means of stimulation
without breaking the skin.
[0013] In 2010, Peters et al. in the Journal of Urology Vol. 183
published results of a randomized clinical trial (RCT) comparing
PTNS with sham treatment in patients with OABS. Two hundred and
twenty (220) adults with OABS were randomized 1:1 to 12 weeks of
treatment with weekly PTNS or sham therapy. Overactive bladder and
QOL questionnaires, as well as 3-day voiding diaries were completed
at baseline and at 13 weeks. Subject global response assessments
were completed at week 13. Results showed PTNS subjects had
statistically significant improvement in bladder symptoms with
54.5% reporting moderately or markedly improved responses compared
to 20.9% of sham subjects from baseline (p<0.001). Voiding diary
measures after 12 weeks found PTNS subjects had significant
improvements in frequency, nighttime voids, voids with moderate to
severe urgency and urinary urge incontinence episodes compared to
sham. Based on the results, researchers concluded PTNS is safe and
effective in treating overactive bladder symptoms.
[0014] MacDiarmid et al. in the Journal of Urology Vol. 183
described the results of the second phase of a study of PTNS for
OAB. The initial study period was 12 weeks. Thirty-two subjects
completed 6 additional months of PTNS therapy and 25 completed the
full 12 months. Outcome measures included voiding diary data,
overactive bladder questionnaires, global response assessments and
safety assessments. Patients received an average of 12.1 treatments
during an average of 263 days, with a mean of 21 days between
treatments. Global response assessments showed sustained
improvement from 12 weeks at 6 and 12 months, with 94% and 96% of
responders, respectively. The authors found the statistically
significant improvements at 12 weeks demonstrated excellent
durability through 12 months.
[0015] The present invention addresses the issues of the prior art
by treating urge incontinence or OAB using a transcutaneous
electrical nerve stimulation device. A method is provided for
same.
[0016] The current accepted form of providing nerve stimulation is
a minimally invasive procedure via an office based implantation of
a stimulation device. Typically, PTNS is a 30 minute office based
treatment via a needle electrode inserted near the tibial nerve,
which carries electric impulses from a hand-held stimulator to the
sacral plexus. Even though the therapy can be clinically effective
with few side effects, the current invasive means of administration
causes it to be expensive mainly due to requiring weekly visits for
administration by a trained professional. Furthermore, as discussed
earlier, difficulty in use and precision control of the therapy
delivery device and some patient discomfort have been known.
[0017] The posterior tibial nerve is a mixed sensory and motor
nerve containing fibers originating from the lumbar and sacral
areas of the spine. The sacral nerves modulate the somatic and
autonomic nerve supply to the bladder and urinary sphincter. The
idea of stimulating the tibial nerve was based on the traditional
Chinese practice of using acupuncture points over the common
peroneal or posterior tibial nerves to affect bladder activity. The
posterior tibial nerve projects to the sacral spinal cord in the
same area where bladder projections are found. These are the areas
where the therapeutic effect of neuromodulation of the bladder
through posterior tibial nerve stimulation takes place. Even though
the exact mechanism of action of neuromodulation is unclear, the
potential benefit of percutaneous or transcutaneous posterior
tibial nerve stimulation is that it may achieve the same
neuromodulatory effect as sacral nerve stimulation through a less
invasive route.
[0018] The present invention provides a safe, reliable, efficacious
and convenient means for treating the condition known as urge
incontinence or OAB. As discussed in the previous section,
transcutaneous electrical nerve stimulation is a proven therapy.
This invention packages this for patient convenience, and is
essentially painless and simple to use. Most importantly, the
device is non-invasive. The device may be strapped (or otherwise
adhered) around or on the ankle, or anywhere along the leg wherein
the tibial nerve may be electrically stimulated transcutaneously.
The device remains in place as the patient ambulates about and
outside of the home. Additionally, the patient may secure the
device in place without clinician or clinic assistance. This allows
the patient with this condition to benefit from the device in the
comfort of his/her own home.
[0019] The non-invasive nature of the invention further makes it
simple to use and does not require administration by a trained
professional, in contrast to other minimally invasive devices on
the market. The non-invasive nature also means that administration
can be performed without requiring the patient to come into a
clinic. This reduces the overall cost of therapy and makes it
accessible to a much larger population who may have previously been
unable to afford a required weekly minimally invasive PTNS
procedure. The device conforms to the contours of the region around
the ankle of the foot to ensure a low impedance electrical conduit
between the electrodes and the skin. This is important to ensure
maximum stimulation.
[0020] Electro-acupuncture or nerve stimulation devices have been
proven effective for the control of nausea and vomiting. An example
of an electro-acupuncture device is described in U.S. Pat. No.
4,981,146 to Bertolucci, marketed under the trademark
Relief-Band.RTM., for control of nausea and vomiting, is worn on
the wrist like a wristwatch, with a watch-like housing which is
positioned on the underside or planar surface of the wrist. A
patient suffering from nausea or vomiting (from motion sickness,
morning sickness, chemotherapy, or anesthesia) can strap the device
onto their wrist and turn it on. When turned on, the device emits
an electrical stimulation pulse over the P6 acupuncture point
(corresponding to the superficial course of the median nerve
through the wrist). Within several minutes, most patients
experience a substantial relief of nausea. Accordingly, there is a
need for non-invasive nerve stimulation devices whereby electricity
is passed through electrodes to stimulate nerves strategically
located within the body, such as a foot or a leg, for
electro-acupuncture or acupuncture treatment of urination related
maladies, including non-limiting examples such as overactive
bladder or incontinence. However, the anatomical structure of the
ankle, within which the tibial nerve is positioned, is quite unique
and different from that of the wrist. Unlike the wrist, the ankle
comprises a boney projection called the malleous which protrudes
outwardly from both the lateral and medial sides of the ankle. In
addition, the unique bone, ligament and tendon structure of the
ankle make adherence of a device difficult. In particular, the area
of depression located between the Achilles tendon and the calcaneus
bone in addition to the boney malleous boney projection of the
ankle make it particularly difficult to adhere a device to the
exterior surface of the ankle so that effective stimulation of the
tibial nerve can be achieved. Therefore, what is needed is a
non-invasive transcutaneous nerve stimulation device that is
conformal to the unique geometry and contours of the ankle region
so that effective stimulation of the tibial nerve in treating over
active bladder can be achieved.
SUMMARY OF THE INVENTION
[0021] The devices and methods described below provide a
non-invasive nerve stimulation or electro-acupuncture device, which
may be used without the application of conductivity gel, or with
minimal application of conductivity gel. The nerve stimulation
device comprises a housing preferably shaped like a watch having a
housing structure that is conformal to the anatomical structure of
the ankle so that the device can be strapped and contactable to a
patient's ankle about the tibial nerve. For the purpose of this
invention, "watch-like" is defined as having a form and structure
comprising a housing, electrodes, a power source and circuitry that
can be worn somewhere on the body, may be conformal to the body
shape to which is it being attached, further attached to a
complementary structure such as a strap, adhesive, stretchable
adhesive, elastomeric film and the like for fastening somewhere on
a body, or carried within a parcel such as a pocket, glove, sock
and the like for locating and affixing somewhere on a body. The
housing is designed to be preferably positioned on the ankle. In
one embodiment, the device comprises a curved underside
specifically designed and dimensioned to fit and conform to the
area posterior or behind the malleolus, or the bony prominence, of
the ankle. The malleolus is present either on the lateral (outer)
or the medial (inner) side of the ankle.
[0022] In another embodiment, the housing is constructed such that
it is flexible and can conform to the shape of the ankle, in
particular, behind the malleolus. In a preferred embodiment, the
housing has a low profile having a relatively thin thickness that
increases the flexibility of the housing. In addition, the device
may comprise a beveled edge to ensure conformity to the curvature
of the ankle. Furthermore, the housing may be composed of a
material that provides increased flexibility such that the device
adheres to the skin of the ankle.
[0023] The housing also encloses a control circuitry and a power
source, such as an electrochemical cell, that powers the device and
provides electrical power for nerve stimulation. The nerve
stimulation device includes electrodes for nerve stimulation. In a
preferred embodiment, the device preferably includes at least one
D-shaped electrode connected to the control circuitry and the power
source. A pair of electrodes is preferably positioned within
respective openings that extend through the curved sidewall of the
bottom surface of the housing of the device. Thus, by positioning
the electrodes within apertures of the bottom curved portion of the
housing, a greater amount of the external surface area of the
electrodes is in direct contact with the curved surface of the
ankle region and positioned over the tibial nerve. As the external
surfaces of the electrodes are in alignment with the contours of
the ankle, more direct contact of the electrode surface with the
skin can be achieved when the housing is worn on the patient's
ankle. A pair of D-shaped electrodes effectively provides
electrical stimulation to the tibial nerve of a patient.
[0024] The nerve stimulation device may also comprise a gasket made
of an electrically non-conductive material such as neoprene or
silicone. The gasket includes two gasket apertures sized and shaped
to receive the electrodes when the gasket is applied to the device.
The gasket provides electrical insulation between the electrodes so
as to prevent a short circuit between the electrodes. The gasket
also acts as a seal between the electrodes and the patient's ankle
to seal in conductivity gel or other conductive material. It will
also serve to retain perspiration in amounts sufficient that the
perspiration itself serves as the conductive material.
BRIEF DESCRIPTION OF THE DRAWINGS
[0025] FIG. 1 illustrates an embodiment of the nerve stimulation
device of the present invention adhered to an ankle of a human.
[0026] FIG. 2 is a diagram of the human leg illustrating the
position of the tibial nerve within the ankle region.
[0027] FIG. 3 is a bottom view of the nerve stimulation device
shown in FIG. 1.
[0028] FIG. 4 is a top view of the nerve stimulation device shown
in FIG. 1.
[0029] FIG. 5 illustrates a side view of the nerve stimulation
device of FIG. 1.
[0030] FIG. 5A is a cross-sectional side view of the nerve
stimulation device shown in FIG. 5.
[0031] FIG. 6 shows a top view of the nerve stimulation device of
the present invention comprising an alternate housing
embodiment.
[0032] FIG. 7 illustrates a bottom view of the nerve stimulation
device of the present invention comprising an alternate housing
embodiment.
[0033] FIG. 8 shows a side view of the nerve stimulation device of
the present invention comprising an alternate housing
embodiment.
[0034] FIG. 9 illustrates an embodiment of an electrical circuit
diagram of the pulse generating circuit of the nerve stimulation
device of the present invention.
[0035] FIG. 10A illustrates an embodiment of an electrical circuit
diagram of an infrared remote control transmitting device that may
be used with the nerve stimulation device of the present
invention.
[0036] FIG. 10B illustrates an embodiment of an electrical circuit
diagram of an infrared remote control receiving device that may be
used with the nerve stimulation device of the present
invention.
[0037] FIG. 11A shows an embodiment illustrating the penetration
depth that is achievable with the nerve stimulation device of the
present invention.
[0038] FIG. 11B shows an embodiment illustrating the penetration
depth achieved with a percutaneous nerve stimulation device of the
prior art.
DETAILED DESCRIPTION OF THE INVENTION
[0039] Now turning to the figures, FIGS. 1, 3-5, 5A and 6-8
illustrate embodiments of an electro-acupuncture or non-invasive
nerve stimulation device 10 of the present invention. In a
preferred embodiment, the device 10 is positionable on an ankle 12
of a patient. As illustrated, the device 10 comprises a housing 14,
which encloses a pulse generator circuit 16 that controls the
operation of the device 10. In addition, a power source 18, such as
an electrochemical cell, is positioned within the housing 14 and is
electrically connected to the pulse generator circuit 16 (FIG. 9).
The electrochemical cell 18 provides electrical power to the device
10 as well as provides a power source for electrical stimulation of
a nerve. The device 10 also comprises at least one electrode that
is configured to be contactable to the skin of a human and
facilitate electrical stimulation. As illustrated, the device 10
preferably comprises two electrodes 20A, 20B that extend through
respective openings of the sidewall of the housing 14 of the device
10.
[0040] As shown in FIG. 1, the nerve stimulation device 10 is
preferably secured to an exterior surface 22 of the ankle 12. In a
preferred embodiment, the device 10 comprises at least one strap 24
that secures the device 10 around the ankle 12 such that the at
least one electrode 20A, 20B is disposed over the tibial nerve 26
(indicated by the phantom line shown in FIG. 2) and in contact with
the skin. As illustrated in FIG. 1, three straps 24 are shown that
secure the device 10 to the ankle 12. In a preferred embodiment,
each of the straps 24 is positioned through a loop 23 that
protrudes from an exterior surface of the housing 14. The loops
fasten each of the straps 24 to the device 10. The three-strap
embodiment shown in FIG. 1 more firmly secures the device 10 to the
ankle 12, which prevents or minimizes dislodgement, displacement or
disengagement of the device from the intended target area, i.e.,
the ankle. It is noted that stimulation of the posterior portion 25
of the tibial nerve 26 (FIG. 2) is a preferred area of nerve
simulation in the treatment of overactive bladder. The posterior
portion 25 of the tibial nerve 26 is positioned on the lateral side
of the ankle 12 and, as such, a preferred location of the device 10
is on the lateral side of the ankle 12 as shown in FIG. 1. Relative
to the ankle, electrode 20A is a distal electrode, located distally
of proximal electrode 20B, so that the electrodes are arranged
along the tibial nerve, with their respective major axes A-A, B-B
aligned with the tibial nerve 26 so that sufficient electrical
power may be transmitted from the electrode 20A, 20B through the
skin to therapeutically transmit a stimulation signal to the tibial
nerve 26. Furthermore, receipt of the signal by the nerve results
in a positive response in managing urination anomalies like
overactive bladder, incontinence and the like. In an embodiment,
the respective major axes A-A, B-B of the electrodes 20A, 20B may
be positioned parallel to, or alternatively, positioned
perpendicular to the tibial nerve 26. The electrodes 20A, 20B are
operably connected to the pulse generator circuit 16 within the
housing 14. During operation, the pulse generator circuit 16
provides electrical stimulation pulses to the electrodes 20A, 20B,
and these pulses are transmitted through the patient's skin to
underlying nerves. The strap 24 can be provided in the form of a
typical non-elastic watchband, a watchband that includes a segment
of elastic material, or it my be comprised of elastic hook and loop
fastener material.
[0041] FIG. 3 illustrates a bottom view of the nerve stimulation
device 10. The electrodes 20A, 20B preferably have a "D" or
semi-circular shape so that the electrodes define straight edges 28
and radial or arcuate edges 30, and are arranged with the straight
edges 28, major axes A-A and B-B, facing each other in opposition.
The electrodes have a radius 32 of about 0.5 inches, but may be
provided in sizes ranging from 0.25 inches to 1.5 inches (about
0.75 to 4 cm). This radius corresponds to the radius of the arcuate
edge 30 in the case where the electrodes are D-shaped, as shown.
The electrodes 20A, 20B however, may be more rectangular, each with
a width of about 0.5 inches (13 mm) and any radius of curvature
which wi11 fit on the chosen housing. The major axis of the
electrodes (corresponding to the straight edge 28 of the
electrodes, and lying transverse to the ankle during use) may be
limited in size in order to conform to the local anatomy of the
ankle, so that it may span the tibial nerve 26. The distal to
proximal width of the electrode array is limited in size so that
the electrodes span a suitable length of the superficial course of
the tibial nerve, but do not overlie more distal and proximal
nerves.
[0042] The electrodes 20A, 20B are separated from each other so
that there is an inter-electrode gap 34 along the opposing straight
edges of the electrodes. The inter-electrode gap 34 separates the
electrodes to prevent a short circuit between the electrodes and
force current flow between the electrodes to flow through the body.
The inter-electrode gap 34 is approximately 0.14 inches wide (3-5
mm), and may range from 0.05 to 0.5 (1-15 mm) in width. The
electrodes 20A, 20B can be manufactured to the appropriate size and
shape by stamping, wherein a sheet of suitable metal is stamped by
a die having the electrode shape.
[0043] The dimensions of the D-shaped electrodes 20A, 20B enhance
the effectiveness of the nerve stimulation device 10. The D-shape
electrodes 20A, 20B are relatively larger in surface area than
conventional electrodes, one example being rounded rectangular or
hot-dog shaped electrodes. When an equivalent electric current is
supplied to the D-shaped electrode and the smaller conventional
electrodes, a lower current density is expected in the larger
D-shaped electrodes. A lower current density should result in less
effective nerve stimulation with our currently preferred power
level (about 10-60 milliamps peak pulse height). The D-shaped
electrodes have a larger surface area than the smaller conventional
electrodes and provide improved current density and improved nerve
stimulation. The improvement is sufficient to allow use of these
electrodes without a conductivity gel, or, concomitantly, use of
the electrodes with conductivity gel but with much lower applied
power. It is not necessary to increase the power level to the
D-shape electrodes to maintain our desired current density. In
addition, an external surface 35 of the electrodes 20A, 20B, which
is contactable to the skin of the ankle 12, may comprise an
electrically conductive material. In a preferred embodiment, the
external surface 35 of the electrodes 20A, 20B may comprise copper,
gold, platinum, an electrically conductive alloy or combination
thereof. The external surface 35 of the electrodes 20A, 20B may be
composed of these materials or, alternatively, may comprise a
coating of these materials. Additional embodiments of the
electrodes 20A, 205 are disclosed in U.S. Pat. No. 6,735,480 to
Giuntoli et al., which is assigned to the assignee of the present
invention and incorporated herein by reference.
[0044] In a preferred embodiment, the size and shape of the housing
14 are substantially determined by: (1) the need to fit comfortably
on the ankle 12, (2) the ability to allow free extension and
flexion of the ankle 12, (3) the capability of concentrating
stimulation over a nerve, in this case the tibial nerve 26
positioned within the ankle 12, and (4) the capacity to be
therapeutic. In addition, the proper fit and conformity of the
device 10 to the body also minimize energy loss and ensure more of
the electrical energy reaches the intended nerve. For example, the
housing is dimensioned to provide effective transcutaneous
stimulation for efficacious therapy of overactive bladder. The
better the fit and conformity of the device 10 to the ankle 12, the
more depth penetration of the electrical stimulation to the nerve
is achieved, and thus an improved therapeutic stimulation results.
In addition, material selection of the composition of the housing
14 is also important to provide a correct fit of the device 10 to
the exterior surface of the body, particularly the ankle 12 which
is more complex in structure, and, in some cases, uniquely
convoluted for certain individuals, in comparison with previous
transcutaneous devices such as wrist stimulators which tend to be
positioned on a planar surface of the wrist. In an embodiment, the
housing 14 is constructed such that it is conformal to the contours
of the ankle 12. As previously mentioned, the unique structural
features of the ankle 12, particularly the boney bump of the
lateral malleolus 36 (FIGS. 1 and 2) that protrudes outwardly on
the lateral side of the ankle 12, make device fit and conformity
particularly difficult. Furthermore, the medial side of the ankle
12 also comprises a boney malleolus which protrudes outwardly from
the ankle 12 which also adds to the difficulties of device fit and
conformity. Optimal fit and conformity of the device 10 to the
intended area, i.e. the ankle 12, is critical in achieving adequate
penetration depth of the electrical stimulation to the targeted
nerve, i.e. the tibial nerve 26, within the body so that optimal
treatment and symptom relief can be provided. In certain cases
wherein the configuration and structure of the intended area are
unique either by origin, accident or defect, a mold of the target
site may be created and then used to fabricate a customized
housing. In addition, conductive gels, adhesives, pastes and the
like may also be used to facilitate improved contact with the
skin.
[0045] Since the device 10 is preferably positioned on the lateral
side of the ankle 12 to stimulate the posterior portion of the
tibial nerve 26, the boney lateral malleolus 36, in addition to the
radius of curvature of the ankle 12, tendons, and ligaments make it
difficult to properly position the device such that it is in
contact with the skin of the ankle. Because of the unique shape of
the ankle 12, the housing 14 is designed to comprise a contoured
curved bottom surface 38 that is conformally positionable adjacent
the lateral malleolus 36 and the posterior portion 25 of the tibial
nerve 26. In addition, the housing 14 may be designed to be
positionable within the depression formed between the calcaneus
bone and the Achilles tendon of the ankle 12.
[0046] In a preferred embodiment, illustrated in FIGS. 3, 4, 5 and
5A, the housing 14 of the device 10 comprises an annular sidewall
40 that provides an exterior housing perimeter. A top surface 42 of
the housing 14, illustrated in FIGS. 4, 5, and 5A, extends from an
upper portion 43 of the sidewall 40 and the bottom surface 38 of
the housing 14 extends from a base portion 44 of the annular
sidewall 40 (FIGS. 5 and 5A). In a preferred embodiment, the
annular sidewall 40 comprises a beveled exterior surface 47 so that
the device 10 is more conformal to the ankle region 12. More
specifically, the bottom surface 38 of the housing 14 preferably
has a convex shape. In a preferred embodiment, the convex bottom
surface 38 has a radius of curvature 46 ranging from about 0.001
inch (0.0025 cm) to about 0.01 inch. (0.025 cm) (FIG. 5A). The
curved convex exterior bottom surface 38 of the housing 14 is
illustrated in the side and cross-sectional views of FIGS. 5 and 5A
respectively. It is this convex exterior bottom surface 38 of the
housing 14 of the device 10 that contacts the exterior surface of
the skin of a patient. More specifically, it is the convex exterior
bottom surface 38 of the housing 14 of the device 10 that contacts
the exterior surface of the skin of the ankle 12 adjacent the
malleolus 36 of a patient.
[0047] In addition, as illustrated in the embodiment shown in FIGS.
4, 5 and 5A, the top surface 42 of the housing 14 is preferably
planar. Furthermore, the top surface 42 of the housing 14 may be
positioned such that it is recessed from a top edge 45 formed by an
end of the upper portion 43 of the sidewall 40 of the housing 14.
This recessed feature of the top surface 42 is designed to prevent
unintentional contact of the control buttons that are positioned
about the top surface 42 of the housing 14.
[0048] As mentioned earlier, in a preferred embodiment, the size
and shape of the housing 14 may be configured by molding the
housing 14 to the specific area of the body to which the device 10
is contactable. For example, the housing 14 may be molded to the
ankle 12 of the patient so that a more exacting fit may be
achieved. In so doing, the housing 14 of the device 10 may be made
of a moldable material examples of which include, but are not
limited to a polymeric material such as, silicone rubber,
acrylonitrile butadiene styrene (ABS), styrene, polycarbonate,
neoprene and combinations thereof.
[0049] As shown, the bottom surface 38 of the sidewall of the
housing 14 comprises a first aperture 48A and a second aperture 48B
through which the respective first and second electrodes 20A, 20B
extend therethrough. In an embodiment, the external surfaces 35 of
the electrodes 20A, 20B are positioned such that they are flush
with the curved bottom surface 38 of the housing 14. Alternatively,
the electrodes 20A, 20B may be positioned within the apertures 48A,
48B so that the external surfaces 35 of the respective electrodes
20A, 20B extend a distance away from the bottom surface 38 of the
housing 14. Thus, by positioning the electrodes 20A, 20B through
the bottom surface 38 of the sidewall 40 of the housing 14, a more
conformal fit of the device 10 can be achieved. More specifically,
by having the electrodes 20A, 20B reside within respective
electrode apertures 48A, 48B, so that the external surface of the
electrodes 20A, 20B are about flush with the curved contour of the
bottom surface 38 of the housing 14, more surface area of the
external surface of the electrodes 20, 20B will be in contact with
the skin of the ankle 12. Therefore, by having an increased amount
of surface area of the electrodes 20A, 20B in more direct contact
with the geometry of the ankle 12, improved nerve stimulation,
particularly that of the tibial nerve 26 can be achieved.
[0050] In addition, a gasket 50 (FIG. 5A) may be positioned around
the perimeter of the electrode 20A, 20B to further secure the
electrode within the respective electrode apertures 48A, 48B. In an
embodiment, the gasket 50 comprises respective gasket apertures
within which electrodes 20A, 20B may be received. The gasket 50 can
be made from any suitable dielectric or electrical insulating
material such as neoprene, silicone, urethane, rubber or other
materials. Thus, the convex shape of the bottom surface 38 of the
housing enables a secure fit of the device 10 and the electrodes
20A, 20B to be positioned adjacent the lateral malleolus 36 of the
ankle 12. Furthermore, the convex shape of the bottom surface 38 of
the housing 14 provides improved contact with the skin of the ankle
12.
[0051] FIGS. 6, 7 and 8 illustrate views of an alternate embodiment
of the housing 52 of the nerve stimulation device 10 of the present
invention. As illustrated, the alternative housing 52 is of a patch
like configuration having a relatively low profile. In a preferred
embodiment, the housing 52 has a curved form with a diameter 54
ranging from about 1.0 inch to about 3.0 inch (FIG. 7) and a
housing thickness 56 ranging from about 0.25 inch to about 1.0 inch
(FIG. 8). This preferred construction of the housing 52 provides
increased flexure of the device 10 around curved radius such as the
boney malleolus 36 of the ankle 12. In a preferred embodiment, the
device 10 has a thickness to diameter ratio ranging from about 1 to
about 3 which enables the housing to bend and conform to the curved
regions of the ankle 12. In addition, the housing 52 of the device
10 may be composed of a polymeric material which includes, but not
limited to, silicone rubber, ABS, styrene, polycarbonate, neoprene
and combinations thereof.
[0052] FIG. 6 illustrates a top view of the alternate embodiment of
the housing 52 and FIG. 7 illustrates a bottom view of the
alternative embodiment of the housing 52. As shown, the housing 52
comprises a top housing or center housing portion 58 that extends
from a bottom housing portion 60. Similar to the previous housing
embodiment 14, the alternative housing embodiment 52, may comprise
a recessed top surface 61 to minimize unintentional contact with
operational control buttons 63. A tab portion 60A may extend
outwardly from the perimeter of the bottom housing portion 60. This
tab portion 60A facilitates application and removal of the device
10 from the skin. In a preferred embodiment, the bottom or center
portion 60 of the housing 52 may be separatable from the top
portion 58 of the housing 52 by pulling tab portion 60A. When
separated, the top or center portion 58 of the housing 58 is left
behind on the skin. In an embodiment, a bottom surface 59 of the
bottom housing portion 60 is contactable to the skin of the ankle
12. In a more preferred embodiment, the electrodes 20, 20B may be
positioned within the bottom surface 59 of the center portion 58 of
the housing 52 so that the external surfaces 35 of the electrodes
20A, 20B are about flush with the bottom surface 59.
[0053] As shown, the top portion 58 preferably comprises a curved
perimeter having a beveled exterior surface 65 and top surface 67.
In a preferred embodiment, illustrated from the side view shown of
FIG. 8, the bottom housing portion 60 comprises an outer perimeter
having a relatively thin perimeter depth. In a preferred
embodiment, the perimeter depth ranges from about 0.25 inch to
about 1.0 inch. This relatively thin depth of the bottom housing
portion 60 in addition to the overall relatively thin housing depth
56 increases the flexibility of the device 10. In other words, the
relatively thin depth of the housing 52 and of the device 10
increases its ability to bend both in left and right and upward and
downward directions.
[0054] FIG. 9 provides an embodiment of a detailed circuit diagram
of the pulse generator circuit 16. The circuit 16 is powered by a
power source 18, such as an electrochemical cell. The cell is
selected on the basis of its capacity rating, which defines the
maximum number of times that the electrotherapy device will
operate. In a preferred embodiment, two CR2025 3 volt lithium coin
cell batteries are connected in series (6 volts total battery
supply). The average current drawn from the batteries is
approximately 0.9 milliamps when delivering therapeutic pulses of
35 milliamps peak pulse amplitude (350 microsecond pulse width at
31 hertz frequency) into a simulated human skin load (500 ohm
resistor). This current draw compares well to the maximum direct
current draw for this type of battery, which is typically 3
milliamps. The typical battery capacity for the CR2025 is 150
milliampere-hours at a continuous electrical current draw of 0.2
milliamperes. A draw of 1 milliamp should produce somewhat less
than 150 hours of battery life.
[0055] As shown in the electrical schematic diagram of FIG. 9, the
power source 18 is connected through switch S.sub.1. Switch S.sub.1
is operable by the patient and enables the patient to turn on and
off the electrotherapy device. Switch S.sub.1 is in the closed
position during operation when the patient has turned on the
electrotherapy device. During operation, the power source 18
discharges pulses into inductor L.sub.1. Inductor L.sub.1 controls
the delivery of current to capacitor C.sub.1 and reduces energy
loss to maximize battery efficiency, C.sub.1 stores the electric
charge and accumulates a corresponding voltage until commanded to
discharge the accumulated voltage to transformer T.sub.1, whereupon
T.sub.1 steps up the voltage for output to the patient in the form
of therapeutic output pulses. Microcontroller 62 controls the
circuit operations. Microcontrollers are typically characterized by
their operating voltage range, their electrical current
consumption, their operating speed (clock rate), the number of bits
used for operations (e.g., 4 bit, 8 bit, 16 bit, etc.), the number
of programmable input/output lines, software program storage space,
and integrated special functions (e.g., A/D converters, high
current source or sink capability, serial communication ports,
etc.). Other factors include cost and availability. 4-bit and 8-bit
microcontrollers are favored due to their small size, low cost, and
low power consumption (e.g., Samsung KS51 series and Toshiba TLCS47
series 4-bit microcontrollers, and Samsung KS86C series, Toshiba
TLCS870 series and Microchip 16C5x series 8-bit microcontrollers).
A preferred embodiment uses a Microchip 16C54A 8-bit
microcontroller.
[0056] Switch S.sub.1 and microcontroller 62 are connected to
transistor Q.sub.1, which together with inductor L.sub.1 comprise a
switched inductor. Microcontroller 62 connects power source 18 to
the inductor L.sub.1 through transistor Q.sub.1, which
microcontroller 62 operates as a switch. The microcontroller 62
repeatedly opens and closes transistor Q.sub.1 to send discharge
pulses to inductor L.sub.1. This causes current to flow into
inductor L.sub.1 and capacitor C.sub.1. Inductor L.sub.1 causes
this current to increase at a controlled rate, thereby causing a
voltage to develop across capacitor C.sub.1 at a controlled rate,
thereby reducing energy losses. When transistor Q.sub.1 is opened,
the current into inductor L.sub.1 begins to decrease. Residual
current in inductor L.sub.1 is then allowed to flow to capacitor
C.sub.1, causing its voltage to increase slightly. Once this
residual current goes to zero, this causes capacitor C.sub.1 to be
isolated in the electrical circuit, thereby preserving the voltage
stored on it. In an embodiment, resistors R.sub.1 through R.sub.5
may provide a discharge path for capacitor C.sub.1 if any of the
switches S.sub.2 are closed. These resistors are chosen to be high
values to limit the discharge current from C.sub.1 to acceptably
low values. The value of inductor L.sub.1 is preferably chosen to
conserve battery life and provide small size and low cost. However,
testing has demonstrated that inductor L.sub.1 can be replaced by a
smaller, lower cost, low value resistor while still obtaining the
advantage of regulated output while the battery voltage decreases
with use. The drawback of this method is that, while battery life
is enhanced vis-a-vis unregulated output, battery life is
compromised vis-a-vis the switched inductor embodiment due to
energy losses in the resistor.
[0057] Inductor L.sub.1 is connected to capacitor C.sub.1, which is
chosen typically to be a high capacitance value to maximize current
storage. Current flowing through inductor L.sub.1 and into
capacitor C.sub.1 causes voltage to build across capacitor C.sub.1
that is proportional to the amount of current delivered over a
particular time period, e.g., the battery discharge time.
Microcontroller 62 monitors the charge/voltage built up on the
capacitor C.sub.1 so it knows when to stop the battery discharge
pulses and/or initiate a transformer discharge pulse (therapeutic
pulse). Low voltage storage capacitor C.sub.1 is connected to
R.sub.1, which together with switch array S.sub.2 and resistors
R.sub.2 through R.sub.5 comprise a voltage divider switching
network. Switch array S.sub.2 is manipulated by the patient to
select one of a number of available "intensity" settings. As shown
in FIG. 9, switch array S.sub.2 selects one of a number of
resistors in a voltage divider array formed by resistor R.sub.1 and
resistors R.sub.2 through R.sub.5.
[0058] R.sub.1 of the voltage divider switching network is
preferably connected to voltage comparator 64. Using the voltage
comparator 64, the microcontroller 62 monitors the voltage across
capacitor C.sub.1, and continues to allow voltage to build until
the voltage comparator 64 signals that the voltage has reached a
predetermined voltage value.
[0059] The next step is to send a therapeutic pulse from the low
voltage storage capacitor to the transformer. The low voltage
storage capacitor is connected to transformer T.sub.1. Transformer
T.sub.1 is chosen to have a voltage step-up characteristic based on
the desired therapeutic output requirements and the load connected
to the electrodes 20A and 20B. Once voltage across C.sub.1 has
reached a predetermined value, microcontroller 62 closes either
transistor Q.sub.2 or Q.sub.3 to discharge the capacitor into the
transformer T.sub.1. This sends the voltage to the output stage to
be stepped up by transformer T.sub.1. In a preferred embodiment,
the transformer has a turns ratio of approximately 20, a low
resistance primary winding (approximately 2 ohms), and a high
inductance secondary winding (approximately 1 Henry). The turns
ratio is selected based on the maximum voltage on the storage
capacitor at the primary and the desired maximum voltage delivered
to the skin through the electrodes at the secondary, e.g., 3 volts
at the primary can deliver 3*20=60 volts at the secondary (other
factors such as transformer core saturation must be considered).
The low resistance primary is needed for reduced power consumption.
The high inductance secondary is needed to achieve a nominally
constant current therapeutic output over a range of skin impedance
values. Skin impedance changes with time for a particular patient,
and can be very different between patients. A nominally constant
current output allows a predictable level of therapeutic current to
be delivered regardless of patient skin characteristics, thereby
providing better therapeutic value.
[0060] Transistors Q.sub.2 and Q.sub.3 are needed to move
electrical current through the transformer T.sub.1 primary winding
in one direction or the other, thereby creating positive or
negative therapeutic pulses at the electrodes 20A and 20B.
Preferably, the microcontroller 62 alternately operates Q.sub.2 and
Q.sub.3 to provide alternately positive and negative pulses to the
electrodes. (Alternating operation of Q.sub.2 and Q.sub.3, together
with a center tap attachment at the center of the transformer
winding, creates a polarity switching circuit which creates the
alternating positive and negative voltage output from the
transformer.) This prevents any iontophoretic or electropheretic
effect on the patient's skin. Alternatively, transformer T.sub.1
can be replaced by a standard transformer to create single polarity
pulses, or it can be removed and the inductor L.sub.1 and capacitor
C.sub.1 chosen to provide the high voltage directly to the
electrodes with a different switching means to effect different
polarity pulses, if required. The operation of transistor Q.sub.2,
Q.sub.3 and Q.sub.1 may be controlled so that the inductor L.sub.1
is always disconnected from the power source 18 when the capacitor
is discharging into the transformer. In this manner, current is
supplied to the transformer only from the capacitor and not from
the electrochemical cell 18.
[0061] The circuit can also create a display to the patient.
Microcontroller 62 may be connected to light emitting diodes (LED)
66 (FIGS. 4 and 6). In a preferred embodiment, a first light
emitting diode 66 may comprise a green LED that is flashed at a low
duty cycle to conserve battery power and is used to indicate normal
operation. A second light emitting diode 66 may comprise a red LED
that is flashed at a faster rate than the first LED and is used to
indicate the "low battery" warning. Alternative display methods may
be used including liquid crystal display, sound, vibration,
etc.
[0062] In a preferred embodiment, capacitor C.sub.1 can be
discharged directly into the skin if certain changes are made to
the circuit. Specifically, a diode can be placed in series between
inductor L.sub.1 and capacitor C.sub.1, which is then chosen to be
a high voltage, high capacitance component, i.e., a standard
"boost" regulator configuration. The diode allows a high voltage to
be stored on the capacitor from a lower voltage source. Resistor
divider values are then chosen to suitably divide the peak high
voltage down to a value suitable for the voltage detector.
[0063] Furthermore, biphasic pulses can be created using capacitor
C.sub.1 as an input to a standard H-bridge transistor circuit with
suitable transistors, with the electrodes connected to the middle
of the H-bridge (the H-bridge is another form of polarity switching
circuit). This method is not preferred because power consumption is
relatively high, resulting in low battery life, and the therapeutic
output becomes nominally constant voltage instead of the preferred
nominally constant current achieved using a transformer or tapped
inductor. However, where the H-bridge is desirable for other
reasons, the battery life may be extended vis-a-vis direct
connection to the battery. Additional preferred embodiments of the
pulse generator circuit 16 are disclosed in U.S. Pat. Nos.
6,076,018 and 7,217,288, both to Sturman et al., and are assigned
to the assignee of the present invention, the contents of which
incorporated herein by reference.
[0064] Furthermore, as illustrated in the electrical schematic
diagram of FIG. 9, the pulse generator circuit 16 may also comprise
a smart electrode assembly 71 comprising electrodes 20A, 20B and
resistor R.sub.6 that is connectable thereto. In this embodiment,
the microcontroller 62 and capacitor C.sub.2 are used to determine
the presence or absence of R.sub.6. When the electrode assembly 71
is connected, the resistor R.sub.6 forms an RC timing circuit in
conjunction with capacitor C.sub.2 in the housing 14, 52. In a
preferred embodiment, the microcontroller 62 is connected to a
parallel RC circuit whose resistance and capacitance are known,
therefore, the RC time constant is known. If the electrode assembly
71 is not connected, the resistance value in the RC circuit is
infinite and the time constant is quite long. If the electrode
assembly 71 is in place, i.e., resistor R.sub.6 is in place, the
voltage is low; if not, the voltage should still be high (that is,
the time constant is long). Thus, the microcontroller 62 can
determine the electrical parameter (resistance of R.sub.6) by
determining the time constant of the RC timing circuit created upon
connection of the electrode assembly to the housing 14, 52 and the
resultant placement of the resistor R.sub.6 into the circuit
16.
[0065] Upon determination of the resistance value of R.sub.6 or the
time constant of the resultant RC timing circuit, the
microcontroller 62 then sets the output range according to a
predetermined schedule which is programmed into the microcontroller
62. For example, the microcontroller 62 and electrode combination
20A, 20B may be set up so that upon sensing the presence of
resistor R.sub.6, the microcontroller 62 will produce a pulsed
stimulation output in a first predetermined output range, while
upon failure to sense resistor R.sub.6 within the electrode
assembly 71 the microcontroller 62 will produce a pulsed
stimulation output in a second predetermined output range.
Different values for the resistance of R.sub.6 may be used to
provide multiple configuration inputs corresponding to multiple
output options. For example, one electrode assembly 71 may use a
certain resistance providing a shorter first time constant, while a
second electrode assembly (not shown) may use a different
resistance resulting in a longer second time constant. The
microcontroller 26 may then be configured to check the capacitor
voltage at the first time constant. If the voltage is still high,
then the microcontroller 26 will check again at the second time
constant for the presence of the second assembly. The number of
different potential values for R.sub.6 will depend on the number of
desired output options, and the resolution of the microcontroller
26 (its ability to discriminate between sensed time constants).
Additional embodiments of RC timing circuits that could be used
with the nerve stimulator device 10 of the present invention are
disclosed in U.S. Pat. No. 6,076,018 to Sturman et al., assigned to
the assignee of the present invention, the contents of which
incorporated by reference.
[0066] In addition, operation of the stimulator device 10 may be
controlled through the use of a remote control. For example, a
remote control operated through infra red (IR), radio frequency
(RF) or telemetry could be used to control the operation of the
stimulation device 10. An example of a transmitting infrared remote
control circuit 68 is given in FIG. 10A. As illustrated, the
circuit 68 comprises a controller 72, capacitors C.sub.3 and
C.sub.4, resistors R.sub.8-R.sub.9 and diode D.sub.3 that are
electrically connected to transmit an infrared control signal. FIG.
10B illustrates an electrical schematic diagram of an example of an
infrared remote control receiving circuit 70. As shown, the circuit
70 comprises a light detecting circuit 74, an electrical power
input and a signal output. Such a remote control receiving circuit
70 could be electrically connected to the pulse generator circuit
16. In a preferred embodiment, an output of the infrared remote
control receiving circuit 70 could be electrically connected to the
micro controller 62.
[0067] In use, the user preferably straps the device 10 onto the
ankle 12 so that the electrodes 20A, 20B overlie the tibial nerve
26. When applied to the ankle 12, the electrodes 20A, 20B are
arranged proximally and distally on the skin of the ankle 12. In a
preferred embodiment, the device 10 is attachable so that it is in
physical contact with the lateral side of the ankle 12.
Alternately, the device 10 could also be attached so that it is in
physical contact with the medial side of the ankle 12. As defined
herein, "lateral side" is the outside side of the ankle that faces
away from the body. The "medial side" is the inside of the ankle
that faces towards the opposite leg. The electronics within the
housing 14 are activated by the user, and are programmed to
generate an electrical pulse pattern. In a preferred embodiment,
the electrical pulse pattern may comprise a 350 microsecond pulse
width at about 31 pulses per second at power levels of about 10-35
milliamps peak pulse height. In addition, power levels of about 40
milliamps peak pulse height to about 80 milliamps peak pulse height
may also be achieved. This pulse pattern is effective to create an
electro-acupuncture effect on the nerve, but other pulse patterns
may also be effective. Additionally, the user may apply gel, and
the device may be programmed to generate pulses at lower power
levels to achieve a similar level of stimulation while reducing
battery consumption. The user need not be overly precise regarding
the placement of the electrodes over the ankle, as the D-shaped
electrodes are much less position sensitive than the conventional
electrodes used in our prior devices. That is, small variations in
the longitudinal and transverse location of the electrodes relative
to the tibial nerve in the ankle do not negatively affect the
transmission of electrical stimulus from the electrodes to the
tibial nerve.
[0068] FIGS. 11A and 11B illustrate the results of computer
modeling that was performed to compare the electrical stimulation,
i.e., voltage potential and electric field as a function of depth
within the skin between the transcutaneous nerve stimulation device
10 of the present invention (FIG. 11A) and a percutaneous nerve
stimulation device (FIG. 11B). The percutaneous device was modeled
to have a needle with a diameter of about 0.25 mm positioned about
1.5 mm within the skin. The output of the transcutaneous nerve
stimulation device 10 of the present invention was modeled to be
about 40 mA constant current and the percutaneous stimulation
device was model to have a constant current output of about 10
mA.
[0069] An equivalent electrical circuit was created to simulate an
anatomical construction having a total tissue thickness of about 15
mm. The modeled anatomical construct comprises a layer of skin,
having a thickness of about 1.5 mm, a layer of fat having a
thickness of about 2.5 mm, a layer of muscle having a thickness of
about 6 mm and bone having a thickness of about 5 mm as a function
of depth extending from the exterior surface of the skin. The
computer model used was based on the work done by Andreas Kuhn
disclosed in his 2008 ETH Zurich PhD dissertation entitled
"Modeling Transcutaneous Electrical Stimulation", the contents of
which are incorporated herein by reference.
[0070] It is important to note that percutaneous electrical
stimulation devices, such as the Urgent PC.RTM. device,
manufactured by Uroplasty.RTM. of Minnetonka Minn. and the
Transtim.RTM. device, manufactured by EMKinetics.RTM.of Mountain
View Calif., are designed to invasively penetrate the skin during
attachment to the intended area being stimulated. In contrast, the
transcutaneous nerve stimulation device 10 of the present invention
does not invasively penetrate the skin but rather is contactable to
the exterior surface of the skin. Furthermore, percutaneous
devices, also in contrast to the present invention, require a
clinician to secure the device, hence the patient must make an
office or clinic visit for the device to be affixed to the body. As
the ankle 12 offers varied articulation of the foot, there is
increased possibility for skin damage or tear under pronounced
movement, such as running, jumping, cycling, dancing, and the like,
which subsequently could lead to infections, cellulitis and other
such complications.
[0071] Specifically, FIGS. 11A and 11B show the electric fields and
associated voltage potential intensities of the transcutaneous and
percutaneous electrical stimulation pulses respectively as a
function of depth in millimeters within the skin of the ankle 12.
As shown, the arrows indicate the direction of the electric field
as it travels within the skin. In a preferred embodiment,
illustrated in FIG. 11A, the electric field travels from a
transcutaneous stimulation "in" position 76, from the first
electrode 20A positioned on the external surface of the skin, to a
transcutaneous stimulation "out" position 78, the second electrode
20B positioned away from the first electrode 20A on the external
surface of the skin. With respect to FIG. 11B, the electric field
travels from a percutaneous stimulation "in" position 80, from a
first needle positioned within the skin to a percutaneous
stimulation "out" position 82, a second needle positioned within
the skin. The intensity of the respective voltage potentials of the
electrical fields shown in FIGS. 11A and 11B are indicated by the
gradient shading shown on the right side of the respective graphs.
As shown, the darker the gradient shading, the higher the voltage
potential at that location within the field.
[0072] As illustrated in FIG. 11A, the transcutaneous input
position 76 of the transcutaneous nerve stimulation device 10 of
the present invention was modeled to comprise a wider input
stimulation region with a higher maximum voltage potential as
compared to the percutaneous input stimulation region adjacent to
the percutaneous input position 80. As shown in FIG. 11A, the
voltage potential was modeled to achieve a maximum voltage of about
0.45 V versus the percutaneous model of FIG. 11B, which indicated a
maximum voltage of about 0.15 V. In addition, as illustrated, the
transcutaneous input region was modeled have a width of about 15 mm
as comparison to about 12 mm for the modeled percutaneous
stimulation device. The wider input region of the transcutaneous
stimulation device 10 of the present invention is mainly attributed
to greater surface area of the substantially "D" electrodes 20A,
20B in comparison to the needle electrodes of the percutaneous
device.
[0073] Furthermore, as shown in FIG. 11A, the intensity of the
voltage potential of the transcutaneous nerve stimulation device 10
of the present invention exhibited less voltage potential decay or
rate of voltage stimulation decline as compared to the modeled
percutaneous stimulation of FIG. 11B. As shown in FIG. 11A, the
voltage potential at about the 15 mm mark of the y axis of the
graph was modeled to be about 0.4 V and the voltage potential at
the 11 mm mark was modeled to be about 0.3 V, thus the rate of
stimulation decay was estimated to be about 0.025 V/mm. In
comparison, the modeled percutaneous device had a voltage potential
of about 0.15 V at the 15 mm mark of the y axis and a voltage
potential of about 0.1 V at about the 14 mm mark, thus the rate of
stimulation decay for the percutaneous device was estimated to be
about 0.05 V/mm or about double the rate of stimulation decay of
the modeled percutaneous device. In addition, the computer modeling
revealed that the rate of decay of the voltage potential is largely
a function of the position of the needle within the depth of the
anatomical construct due to the difference in electrical
resistivity of the various layers. Specifically, the computer
modeling revealed that positioning the needle of the percutaneous
device at a depth of about 6 mm within the body, resulted in an
even greater rate of voltage potential decay. Thus, the need to
precisely position the needle of the percutaneous device in
providing effective electrical stimulaton is particularly
critical.
[0074] Based on the computer modeling analysis illustrated in FIG.
11A, the transcutaneous nerve stimulation device 10 of the present
invention is well suited in establishing an electric field and
current density to stimulate a nerve, preferably the tibial nerve
26 positioned within the body. As previously mentioned, the
transcutaneous nerve stimulator device 10 of the present invention
is positioned on the external surface of the skin in contrast to a
percutaneous stimulation device having a relatively small needle
that is positioned within the skin. The wider electric field and
higher voltage potential in combination with the increased surface
area of the "D" electrodes, enable the nerve stimulation device 10
of the present invention covers a greater area and can be
positioned by the user of the device. In contrast, because the
percutaneous stimulation devices comprise relatively small needles,
the device must be precisely positioned by a clinician to achieve
effective nerve stimulation. In addition, the increased rate of
decay of the voltage potential of the percutaneous devices,
particularly at differing depths within the skin, increases the
need to precisely position the needle within the body to achieve
optimal stimulation. If the needle of the percutaneous device is
not properly positioned, effective nerve stimulation may not be
achieved. Furthermore, if the needle of the percutaneous device
were to become dislodged, moved from its intended position, or
unintentionally driven further into the skin, effective nerve
stimulation might be lost. Consequently, the loss of effective
nerve stimulation requires a trip to the clinic or hospital for
clinician repositioning and re-engagement of the needle. The
present invention with the increased surface area of the electrodes
resolves this issue by delivering consistent therapy via the wider
electric field, higher voltage potential and less voltage potential
decay through the depth of the tissue to the tibial nerve 26.
[0075] In summary, the electrical nerve stimulation device 10 of
the present invention provides a wider and deeper field of
stimulation with less decay as compared to the percutaneous method
of the prior art. This improvement in electrical stimulation
consistency and penetration, in addition to a wider cross-sectional
penetration width, that is achieved by the device 10 of the present
invention, increases exposure of the targeted nerve to the
stimulation pulse thereby providing improved efficacious therapy.
Further contributing to the effectiveness of the therapy delivery
to the tibial nerve 26 positioned within the ankle 12, is the
improved conformal fit of the housing 14, 52 of the device 10 of
the present invention, further improves penetration depth of the
electrical stimulation to the tibial nerve 26. Because of the
curved, convex shape of the outer surface of the housing 14, 52,
the electrodes 20A, 20B of the nerve stimulation device 10 of the
present invention offers more intimate contactability to the
exterior skin surface 22 of the ankle 12 augmenting nerve
stimulation treatment for example, enhanced and even more efficient
overactive bladder treatment.
[0076] While the preferred embodiments of the devices and methods
have been described in reference to the environment in which they
were developed, they are merely illustrative of the principles of
the inventions. Other embodiments and configurations may be devised
without departing from the spirit of the inventions and the scope
of the appended claims.
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